Figure 3-11.A typical electronic multimeter.precautions and requirements for quality assuranceverification.Personnel involved in troubleshooting and per-forming operational checks should consult the recordsmaintained in maintenance control and/or the workcenter register. Reference to records of previousmaintenance may show a progressive deterioration of aparticular system or a previous discrepancy. Thisprocedure could be helpful in pinpointing the cause ofthe malfunction currently being experienced.ELECTRICAL FAILURESSince practically all systems now have someelectrically controlled components, troubleshootingmust also include the related electrical circuits in manyinstances. Although an AE is generally called upon tolocate and correct electrical troubles, you should be ableto check circuits for loose connections and even performcontinuity checks when necessary. Therefore, aknowledge of electrical symbols and the ability to readcircuit diagrams is necessary. Figure 3-4 illustrates theelectrical symbols commonly found in schematicdiagrams.Loose connections are located by checking allconnectors in the circuit. A connector that can be turnedby hand is loose and should be tightened hand tight.A continuity check is simply a matter ofdetermining whether or not the circuit to the selectorvalve, or other electrically controlled unit, is complete.Continuity checks are made with the use of a multimeter.The name multimeter comes from MULTIPLEMETER, and that is exactly what a multimeter is. It is adc ammeter, an ac ammeter, a dc voltmeter, an acvoltmeter, and an ohmmeter, all in one package. Figures3-10 and 3-11 show the faces of commonly usedmultimeters. The applicable instructions should beconsulted prior to equipment operation.TORQUING OF FASTENERSLearning Objective: Recognize the importanceof the proper torquing of fasteners and therequired torquing procedures.Fastener fatigue failure accounts for the majority ofall fastener problems. Fatigue breaks are caused byinsufficient tightening and the lack of proper preload orclamping force. This results in movement between theparts of the assembly and bending back and forth orcyclic stressing of the fastener. Eventually, cracks willprogress to the point where the fastener can no longersupport its designed load. At this point the fastener failswith varying consequences.TORQUING PROCEDURESFor the nut to properly load the bolt and preventpremature failure, a designated amount of torque mustbe applied. Proper torque reduces the possibility of thefastener loosening while in service. The correct torqueto apply when you are tightening an assembly is basedon many variables. The fastener is subjected to twostresses when it is tightened. These stresses are torsionand tension. Tension is the desired stress, while torsionis the undesirable stress caused by friction. A largepercentage of applied torque is used to overcome thisfriction, so that only tension remains after tightening.Proper tension reduces the possibility of fluid leaks.3-19